Contact member for semiconductor translating device



March 8, 1960 D. E. IGLESIAS 2,928,031

Y CONTACT MEMBER FOR SEMICONDUCTOR TRANSLATING DEVICE Filed Sept. 4,1958 FIG.

43 FIG. 3

D. E IGLES/AS l I L' d. W

AT TORNEV CONTACT MEIVIBER FOR SEMICONDUCTOR TRANSLATING DEVICE David E.Iglesias, Maplewood, N.J.,- assignor to Bell Telephone Laboratories,Incorporated, New York, N.Y.,acorporation of New York E ApplicationSeptember 4, 1958, Serial No.'758,996

' I 4 Claims. (Cl. 317234).

This invention relates to semiconductor translating devices, and moreparticularly to an element for providing electrical contact to the smallarea mesa of a silicon or germanium diffused diode.

tion of, a pin type structure substantially limits the inductance of thecontacting element.

fact has been established therewith, the contact element.

Both the semiconductor device and the contacting ele- 1 ment are mountedin a compact supporting structure. The pin-diaphragm contact element ispositioned against the mesa of the device, and after secure electricalconis held permanently in place by the-use of set screws Since theforming of the diaphragm curvature durmg the welding step isaccomplished simply by the use of av welding rod with a concave tip, themanufacture of these contact elements is quite simple. Furthermore,since the flexible diaphragm is spot welded to a rigid pin member, theentire contacting element is capable of easy handlingand storage beforeassembly, and the danger of deforming the element is substantiallyreduced.

Silicon or germanium diffused diodes as presently constructed consist'ofa base wafer with a projectionor mesa on one face thereof, the mesacontaining the rectifying junction between the pand n-type materials ofwhich the diodeis composed; The mesa is typically 0.001 inch high with acircular top surface 0.001 inch in diameter. The base wafer isordinarily of the same shape, being however, about four times as thickas the mesa and having a diameter about thirty times as great. Providingelectrical contact to the mesa of a silicon orrgerr'nanium difiuseddiode has presented many problems. Since the mesa is of small size,barely if at all perceptible with the naked eye, positioning anelectrical lead or sharp point-contacttype of element thereon requiresgreat precision. Two other major considerations also present themselves.First, the contacting element must be resilient enough so as not tostrain the mesa or,

While satisfying the requirement In positioning the diaphragm upon themesa, no portion of the curved diaphragm should touch the surroundingwafer surface, or a shorting out of the diode will result. given 'rnesasize, there will be a certain area of the diaphragm on whichfcontactwith the mesa may be made without shorting out the diode. By choosingthe curvature of the diaphragm accordingly, the degree of accuracyrequired for such a positiomng may be substantially reduced and theallowable contacting surface area of the diaphragm may be made manytimes the area of the mesathat is to be contacted. Thus, the difficultyheretofore encountered in positioning thin wire leads and sharppoint-contact types of contacting elements upon the small area mesas ofgermanium or silicon diffused diodes is substantially eliminated.

Thus, a feature, of the present invention is amesa contacting elementcomprising a conductive pin member having secured to one end thereof aflexible conductive diaphragm, whereby a contacting structure possessingboth low inductance and high resiliency is provided.

The invention may bebetter understood by consultingthe followingdescription of which the accompanyingdrawing is a part, and in which:

. Fig. 1 depicts in partial section'a contacting element made inaccordance with the principles of the present invention;

. Fig. 2 depicts in perspective a welding jig designed for welding thediaphragm to the pin and for simultaneously forming the curvature of thediaphragm;

such structures do not satisfy the aforementioned flexi bilityrequirement.

An object of the present invention is a contacting element for the smallarea mesa of a semiconductor translating device, which element ischaracterized by both low inductance and a high degree of resiliency.

Another object'of this invention is a contacting ele- I, end, and is theportion of the contacting element designed to come into direct contactwith the mesa of a translatingdevice. During the welding process, thediaphragm assumes a convex outward shape with respect to the pin end. Itis this resilient diaphragm that provides the flexibility of thecontacting member and which protects against stress and strain producedby rnechanical shock and. temperature change. At the same time, theutiliza- Fig. 2A depicts in perspective a:welding electrode with,

aconcave tip used to form the curvature of the diaphragm; r

Fig. 3 depictsin perspective a typical diode; and

Fig. 4 depicts in perspective and in'partial section a diode anditsassociated contacting element mounted in a supporting structure.

Referring to Fig. 1, the contacting element 11 comprises a machined pin12 composed of nickel or any other material having" similar electricalcharacteristics and. capable ofbeing welded. Pin length and diameter aredictated by the inductance and resistivity requirements ofthe'contacting element, and by the size and characteristics of. thesupp'ortingstructure of the diode and its mesacontacting elementf It istobe noted that contact element.

resilience is in no way dependentupon pin length; Therefore, in order toeffect the greatest reduction in contact element inductance, pin lengthshould bejkept as-short as possible. For diodes with wafer and mesasizes of the order above mentioned, the contacting element in onespecific instance was composed of a pin of 0.37 5'inch in length, with adiameter of 0.050inch.

Advantageously, one 'end ofthe' pin" 12 is bored, thus: leaving a thincylindrical; wall 13. This thin wall serves} two purposes. IFirstjafbetter weldingxedge is obtained?" Patented Mar. 8, 1960.

Thus, for a given diaphragm curvature and a.

3 second, a greater inside diaphragm area is achieved, therebypermitting better diaphragm action. In the specific instance mentionedabove, the bore had a diameter of 0.043 inch and extended 0.031 inchinto the pin.

A thin diaphragm 14 is welded or otherwise suitably bonded to the end ofpin 12 which contains the bored hole 15. In one specific instancethediaphragm was composed of Nilvar, a nickel alloy composed of 31 percentnickel, 4 percent cobalt, and 65 percent iron. This particular alloy hassuificient hardness to give good spring action as a diaphragm. Squaresabout one-eighth of an inch on a side were cut in advance of the weldingstep, but a strip of foil, for example, could be used in an automaticprocess. The diaphragm thickness is dictated by the resiliencerequirement of the contacting element. In the specific embodiment of theinvention mentioned above, the diaphragm was 0.001 inch thick.

he curvature of the diaphragm 14, which is convex outward with respectto the rod end to which it is at tached, is dictated mainly by the sizeof the mesa and the achievable degree of accuracy in positioning thediaphragm upon the In positioning the diaphragm upon the mesa, care mustbe taken so as not to allow the diaphragm to short out the diode bytouching the base wafer. Shorting occurs with a diaphragm of ,a givencurvature b not ositioning the dia hragrn center oint directly over themesa. Therefore, the amount of allowable oii-center positioning of thediaphragm is governed by diaphragm curvature for any particular mesasize. Accordingl the diaphragm curvature should be chosen such that easyand relatively noncritical, positioning of the diaphragm on the mesa maybe attained; In one specific embodiment of the invention, the radius ofcurva ture for a pin of the size above mentioned was approximately 7 ofan inch. 2

Referring to Fi". 2, there is depicted a welding jig 21 designed forwelding the diaphragm 14 to the pin 12 and for simultaneously formingthe diaphragm curvature. The pin 12 with its bored end upward is placedin a hole 22 in one of the weldingelectrodes 23. A rod 24 forms theother welding electrode. The rod 24, as depicted also in Fig. 2A, has aconcave end portion 25 with a curvature similar to that'desired forthe'diaphragm. The diameter of the rod 24 at the concave end portion 25is slightly larger than that of the pin 12. The rod 24 is positioned.over the pin 12 by a hole 26 in the welding electrode 23. The welding"electrode 23 also acts as a'supporting structure for the weldingelectrode 24. The two electrodes, it is noted, are insulated from eachother by a Bakelite or similar insulator 27. A piece of foil 28 that isto form the diaphragm 14 is positioned over the pin 12, and the weldingelectrode 24 with its concave end downward is brought down upon the foiland the pin 12. The two electrodes are attached to a welding machine andthe foil 23 is welded to the pin 12. During the welding process, byvirtue of both the pressure of the rod 24 upon the foil 28 and the pin12, and the heat of welding, the foil 28 assumes the curvature of theconcave portion 25 of the welding electrode 24. In such a manner thediaphragm 14 is welded to the pin 12 and is automaticallygiven therequired amount of curvature.

After welding is completed the excess diaphragm material is removed. Aplunger maybe used in conjunction with the welding jig for this purpose.The plunger, which may be made of hardened drill rod, is bored in oneend with a hole of a diameter slightly greater than that of the pin '12.The welding electrode 24 is removed from the jig and the plungersubstituted therefor, with its bored end downward. By driving theplunger downward and over the end of pin 12, the excess diaphragmmaterial is sheared off. If this operation is done immediately after thewelding operation, the pin 12 does not have to be removed from theWelding jig. Thereafter,

the. edges. of the pin may be polished. .Advantageously,

holder before these are screwed into the ceramic strucare thentightened.

2,928,031 a a f both the pin and the diaphragm may be electroplated withgold or a similar material in order to reduce skin efiect losses.

Fig. 3 depicts a typical diode 31, comprising a base portion 32, whichmay be of silicon or germanium, and a mesa 33. The diode and its mesacontacting element may be assembled together in a compact supportingstructure as illustrated in Pig. 4. The diode 31 containing the mesa 33is soldered or otherwise affixed to a,

metal stud 42. The stud with the water is screwed into one end of aninsulating ceramic structure 43, and a metal pin holder 44 is screwedinto the other endof the ceramic insulating structure. It is noted thata small amount of polystyrene cement or similar material may be appliedto the threads of the stud and the pin ture to insure that the threadedjoints Will remain tight and not loosen.

Next, in assembling a device illustratively embodying the principles ofthe present invention, the contact ele:

' ment 11 is placed in the pin holder, and is allowed to slide all theway against the mesa. The set screws 45' The unit is now ready fordeflection of the diaphragm against the mesa. This may be accomplishedby use of a device developed by H. C. Theuerer, which is described onpage 326 of Crystal Rectifiers by H. C. Torrey and C. A. Whitmer, volume15 of the Radiation Laboratory Series.

Briefly, then, the deflection instrument comprises a micrometer and areductiongear box. The micrometer is utilized to drive the pin 12 of thecontact element 11, while the purpose of the gear box is toootain a finemotion of the pin 12, so that the deflection of the dished diaphragm 14can be closely controlled. The point of final deflection of thediaphragm may be determined by the use of an oscilloscope presentationof current-voltage characteristics. More specifically, electricalconnections are made to the diode and an oscilloscope, and theoscilloscope monitors the instant that contact is made withthe mesa.After such a contact, and after the electrical characteristics of thediode are determined to be as required, the diaphragm of the contactelement may be deflected against the mesa' Final deflection of thediaphragm is undertaken so as to assure that the diaphragm isresiliently biased against the mesain order to provide aspringtypecontact. After. final deflection has been achieved,

stud respectively.

It is to be understood that the above-described. embodiment is merelyillustrative of the apphcations of the principles of the-presentinvention. Other arrangements may. be easily made by those skilled inthe art without departing from the spirit'and scope of this invention.

What is claimed is: v

1. A semiconductor translating device comprising a semiconductive wafer,said wafer having a raised portion of reduced area on one face thereof,a contact member for contacting the surface of said raised portion, saidcontact member comprising a rod having a hollowed out portion at one endadjacent said water and av dished metal diaphragm affixed to saidhollowed out end, and mounting means for supporting said water and saidcontact member.

raised portion thereon, a

contact member adjacent said raised portion,..and mount-.

7 ing means for supporting said wafer and said member in contactingrelationship.

3. A semiconductor translating device in accordance with claim 2 whereinsaid contact member is coated with a conducting material of greaterconductivity than the diaphragm material and the rod material.

4.- A semiconductive translating device comprising a semiconductivewafer, a contact member for contacting the surface of said wafer, saidcontact member comprising a rod and a diaphragm aflixed to one end ofsaid rod,

said diaphragm haying aconvex outward shape with respect to the rodendtowhich it is attached and being that 7 References Cited in the file ofthis patent UNITED STATES PATENTS 2,569,570 Matare et a1. Oct. 2, 1951Jacobi Dec. 27, 1955

